Aberrant Notch signaling has been linked to many cancers including choroid plexus (CP) tumours, a group of rare and predominantly pediatric brain neoplasms. We developed animal models of CP tumours by inducing sustained expression of Notch1 that recapitulate properties of human CP tumours with aberrant NOTCH signaling. Whole transcriptome and functional analyses showed that tumour cell proliferation is associated with Sonic Hedgehog (Shh) in the tumour microenvironment. Unlike CP epithelial cells, which have multiple primary cilia, tumour cells possess a solitary primary cilium as a result of Notch-mediated suppression of multiciliate diffferentiation. A Shh-driven signaling cascade in the primary cilium occurs in tumour cells but not in epithelial cells. Lineage studies show that CP tumours arise from mono-ciliated progenitors in the roof plate characterized by elevated Notch signaling. Abnormal SHH signaling and distinct ciliogenesis are detected in human CP tumours, suggesting SHH pathway and cilia differentiation as potential therapeutic avenues.

Mentions:
The similarity in gene expression between tumour and roof plate cells, together with elevated Notch signaling and solitary primary cilium in the latter, suggests that Notch-induced CP tumour is related to the roof plate. To delineate the developmental origin of CP tumour, we first analyzed the distribution of Atoh1+ progenitors in hindbrain roof plate using Math1M1GFP mice with enhanced green fluorescent protein (EGFP) fused to the C-terminal of Atoh143. In addition to rhombic lip, Atoh1:EGFP+ cells are present in the Lmx1+/Otx2+ upper roof plate but largely absent from lower roof plate (Fig. 7a, Supplementary Fig. 8a). Second, we analyzed tumour formation in Mcre;NICD1 animals during development. At day E12.5, though many NICD1+/GFP+ cells are located in rhombic lip bordering Lmx1a+ roof plate, some NICD1+/GFP+ cells are present within CP forming into papillary structures (Fig. 7b). These prospective Lmx1a+ tumour cells undergo proliferation (Ki-67+), and remain undifferentiated (Aqp1−) (Fig. 7b, Supplementary Fig. 8b). At day E14.5, most NICD1+/GFP+ tumour cells are found in Lmx1a+ upper roof plate and rostral half of the CP (Fig. 7c). Third, proliferative progenitors (Lmx1a+/Ki-67+/Aqp1−) in hindbrain roof plate differentiate into post-mitotic epithelial cells that form the CP epithelium (Lmx1a+/Ki-67−/Aqp1+) during embryogenesis44, 45. The shape and size roof plate are similar between wild type and Mcre;NICD1 mice; however, tumour cells remain proliferative and undifferentiated (Ki-67+/Aqp1−) even after their incorporation into CP epithelium (Fig. 8a, Supplementary Fig. 8c). Together, these results indicate that CP tumours in these animals arise from roof plate progenitors and migrate into the CP where they continue to undergo Shh-driven proliferation throughout development (Fig. 8b, 8c).

Mentions:
The similarity in gene expression between tumour and roof plate cells, together with elevated Notch signaling and solitary primary cilium in the latter, suggests that Notch-induced CP tumour is related to the roof plate. To delineate the developmental origin of CP tumour, we first analyzed the distribution of Atoh1+ progenitors in hindbrain roof plate using Math1M1GFP mice with enhanced green fluorescent protein (EGFP) fused to the C-terminal of Atoh143. In addition to rhombic lip, Atoh1:EGFP+ cells are present in the Lmx1+/Otx2+ upper roof plate but largely absent from lower roof plate (Fig. 7a, Supplementary Fig. 8a). Second, we analyzed tumour formation in Mcre;NICD1 animals during development. At day E12.5, though many NICD1+/GFP+ cells are located in rhombic lip bordering Lmx1a+ roof plate, some NICD1+/GFP+ cells are present within CP forming into papillary structures (Fig. 7b). These prospective Lmx1a+ tumour cells undergo proliferation (Ki-67+), and remain undifferentiated (Aqp1−) (Fig. 7b, Supplementary Fig. 8b). At day E14.5, most NICD1+/GFP+ tumour cells are found in Lmx1a+ upper roof plate and rostral half of the CP (Fig. 7c). Third, proliferative progenitors (Lmx1a+/Ki-67+/Aqp1−) in hindbrain roof plate differentiate into post-mitotic epithelial cells that form the CP epithelium (Lmx1a+/Ki-67−/Aqp1+) during embryogenesis44, 45. The shape and size roof plate are similar between wild type and Mcre;NICD1 mice; however, tumour cells remain proliferative and undifferentiated (Ki-67+/Aqp1−) even after their incorporation into CP epithelium (Fig. 8a, Supplementary Fig. 8c). Together, these results indicate that CP tumours in these animals arise from roof plate progenitors and migrate into the CP where they continue to undergo Shh-driven proliferation throughout development (Fig. 8b, 8c).

Aberrant Notch signaling has been linked to many cancers including choroid plexus (CP) tumours, a group of rare and predominantly pediatric brain neoplasms. We developed animal models of CP tumours by inducing sustained expression of Notch1 that recapitulate properties of human CP tumours with aberrant NOTCH signaling. Whole transcriptome and functional analyses showed that tumour cell proliferation is associated with Sonic Hedgehog (Shh) in the tumour microenvironment. Unlike CP epithelial cells, which have multiple primary cilia, tumour cells possess a solitary primary cilium as a result of Notch-mediated suppression of multiciliate diffferentiation. A Shh-driven signaling cascade in the primary cilium occurs in tumour cells but not in epithelial cells. Lineage studies show that CP tumours arise from mono-ciliated progenitors in the roof plate characterized by elevated Notch signaling. Abnormal SHH signaling and distinct ciliogenesis are detected in human CP tumours, suggesting SHH pathway and cilia differentiation as potential therapeutic avenues.